The invention relates to a camshaft for actuating the gas exchange valves of an internal combustion engine, having a camshaft tube, a hydraulic camshaft adjuster, a valve for controlling the hydraulic fluid supplied to the camshaft adjuster and an actuating device disposed in the interior of the camshaft tube for actuating the valve which is secured in the axial direction to prevent displacement.
PCT International Publication No. WO 2009/009328 A1 discloses a camshaft having an actuating device formed as an electromagnet (solenoid) that does not rotate along with the camshaft tube when the camshaft rotates. The solenoid is disposed so as to always be fixed to the cylinder head, i.e., it is fixedly connected to the cylinder head of the engine. Two different embodiments are described, showing how the solenoid can be disposed in the interior of the camshaft. In accordance with a first embodiment, the solenoid is mounted via a bearing element disposed in the interior of the camshaft tube and is fixedly connected to the cylinder head of the engine via a tubular connecting element and an end piece. Reference is made to the fact that the connecting element (“tubular shaft” or “torque tube” 116) can also be used for guiding cables for supplying current to the solenoid. In accordance with a second embodiment, the solenoid has an increased length compared with the first embodiment and is itself directly attached to the cylinder head/engine block of the engine which means that there is no need to provide the bearing element required for the first embodiment or to provide the tubular connecting element.
The solutions for disposing the actuating device in the interior of the camshaft tube known from PCT International Publication No. WO 2009/009328 A1 have, inter alia, the disadvantage that virtually the entire interior of the camshaft tube is taken up either by the tubular connecting element (embodiment 1) or by the lengthened solenoid (embodiment 2) and thus cannot be used for the integration of further components (such as for example oil separating devices for purifying blow-by gas) or for other uses. Therefore, further functional elements can no longer be integrated into the interior of the camshaft tube. In the case of embodiment 1, inner-working of the camshaft tube is also required due to the bearing element disposed in the interior of the camshaft tube, in order to satisfy the high precision requirements for proper accommodation of the bearing. The total weight of the known camshaft is also high due to the connecting and bearing elements for holding the solenoid or the increased length of the solenoid.
A further disadvantage of the solutions known from PCT International Publication No. WO 2009/009328 A1 is that due to the holding and connecting elements, by means of which the actuating device is held in the interior of the camshaft tube and is connected to the cylinder head, an oil pump or vacuum pump is not disposed on the end of the camshaft opposite the camshaft adjuster and cannot be driven via the camshaft.
Exemplary embodiments of the present invention provide a camshaft for actuating the gas exchange valves of an internal combustion engine having a low weight and in which in addition to the actuating device and possibly the valve still further functional elements can also be integrated into the interior of the camshaft. It should also be possible to dispose an oil or vacuum pump—which can be driven by the camshaft—on the end of the camshaft opposite the camshaft adjuster.
In accordance with the invention, the actuating device for actuating the valve is formed as an electromagnetic or piezoelectric actuating device and is connected to the camshaft tube in a rotationally-fixed manner. Therefore, the actuating device in the present invention rotates along with the camshaft and no separate holding and connecting elements for holding the actuating device in the camshaft tube and for attaching it to the cylinder head are required. It is also not necessary to increase the length of the actuating device in the axial direction in order to attach it directly, i.e., without separate holding and connecting elements, to the cylinder head/engine block. The interior of the camshaft tube located next to the actuating device remains free and can be used for incorporating other functional elements into the camshaft or for other uses.
Considerable weight savings are achieved because separate holding and connecting elements are no longer needed and the actuating device no longer needs to be lengthened in the axial direction and be directly attached to the cylinder head/engine block. A bearing element disposed in the interior of the camshaft tube for accommodating the actuating device is not required in the solution in accordance with the invention which means that in this respect weight and costs (in particular material and production costs) are also saved by the invention.
In the case of the invention, an oil or vacuum pump—which can be driven by the camshaft—can readily be disposed on the end of the camshaft opposite the camshaft adjuster. As a result, the designer has more options for exploiting the drive energy provided by the camshaft rotation compared with the solution known from the Prior Art.
In accordance with one embodiment of the invention, the actuating device is press-fitted into the interior of the camshaft in a non-positive locking manner or in a positive locking manner or in a non-positive and positive locking manner. In this case, the actuating device cannot be removed from the camshaft tube, or can only be done so with a great deal of difficulty, when it is defective for example. If the actuating device is defective, generally the entire camshaft must then be replaced. In order to avoid this, provision can be made in accordance with the invention to form the connection between the actuating device and the camshaft tube as a releasable connection. Such a releasable connection can be for example a latching connection or a screw connection.
In order to be able to supply current to the actuating device, current supplying means are provided in the interior of the camshaft tube and are connected thereto in a rotationally-fixed manner. These means can be formed for example as electric lines which are connected on the one hand to the camshaft tube and on the other hand to the actuating device.
In accordance with one embodiment of the invention, the current is fed to the current supplying means via elements connected to the camshaft tube in a rotationally-fixed manner. These elements can be disposed for example on the outer periphery of the camshaft tube or in the interior of the camshaft tube. For instance, the elements can be formed for example as annular brushes, slip rings or induction coils.
Stationary means can be allocated to the elements connected to the camshaft tube in a rotationally-fixed manner, wherein by virtue of the stationary means the current for powering the actuating device is transferred to the elements rotating along with the camshaft or is inducted in these elements. These stationary means can be formed for example as stationary brushes, sliding contacts or electromagnetic coils.
In terms of the current transfer, provision can be made in accordance with the invention that the elements connected to the camshaft tube in a rotationally-fixed manner comprise transmitter elements and the stationary means comprise sensor elements of a camshaft position determining device. In this manner, the components required for the current transfer can simultaneously be used to form a position determining device for determining the rotational position of the camshaft which is in any case required for most applications.
In accordance with a further embodiment of the invention, the valve is also disposed in the interior of the camshaft tube and is connected thereto in a rotationally-fixed manner. Owing to the fact that the valve is also integrated into the interior of the camshaft tube, the actuation of the valve by the actuating device is facilitated and the axial constructional space required for the camshaft can be further reduced.